This application is based on application No.11-90965 filed in Japan on Mar. 31, 1999, the content of which incorporated hereinto by reference.
This invention relates to a thermostat that cuts off electrical current when the ambient temperature exceeds a set temperature and to a battery pack that contains the thermostat. In particular, this invention relates to a thermostat in which the thermostat return temperature when the ambient temperature drops after it has reached a high temperature and current has been cut off can be varied depending on the rising temperature and to a battery pack that contains the thermostat.
A thermostat which cuts off current when the ambient temperature exceeds a set temperature is housed, for example, in a battery pack, and cuts off current to protect the batteries when the temperature exceeds a set temperature. Further, the thermostat is housed not only in a battery pack but also an electric appliance containing a heater. The thermostat housed in an electric appliance cuts off current when the ambient temperature exceeds a set temperature and returns to the on state and turns on current when the ambient temperature drops.
The thermostat cuts off current when the ambient temperature exceeds a set temperature, and then it returns to the on state and turns on current when the temperature drops. When the ambient temperature becomes even higher than a set temperature due to an accident to a battery pack and an electric appliance, current should be maintained in a cut-off state for safety""s sake. To realize this, a thermostat and a thermal fuse are combined to use. The blowout temperature of thermal fuse is set at a higher temperature than the thermostat cut-off temperature. When the ambient temperature becomes abnormally higher than a set temperature, the thermal fuse is blown out and current is maintained in the cutoff state.
This circuit is safe to use, but has the drawback that parts assembling requires much time and labor and the manufacturing cost is high because two parts of the thermostat and fuse are installed, and also it is difficult to miniaturize because the two parts are installed respectively.
To solve these problems, a thermostat that maintains current in the cut-off state after the ambient temperature has risen abnormally was developed (Japanese Non-examined Patent Publication HEI 8-7729). As shown in a cross-section view of FIG. 1, a thermostat described in this publication contains fuse springs 9. The fuse springs 9 are fixed by thermal deformation materials 10 such as an alloy easily melted and synthetic resin. When the thermal deformation material 10 of synthetic resin fixing the fuse springs 9 is heated to a higher temperature than the thermostat cut-off temperature, it can not maintain the fuse springs 9 due to deformation. When the thermal deformation material 10 becomes in this state, the fuse springs 9 push a movable contact 3, and the thermostat is maintained in the off state. The number of 4 shows a fixed contact in this figure.
The thermostat, shown in FIG. 1, maintains the movable contact 3 in the off state when the thermal deformation material 10 can not maintain the fuse springs 9 due to thermal deformation. Therefore, the thermostat can be so structured as not to return to the on state when the ambient temperature rises abnormally. However, a thermostat with this structure requires thermal deformation materials such as an alloy easily melted and synthetic resin which deform surely to disengage a fixed condition of the fuse springs when the ambient temperature exceeds a set temperature. For this reason, the manufacturing cost is increased. Further, it is necessary for the thermal deformation material to maintain the fuse springs firmly when the ambient temperature is lower than a set temperature. However, the thermal deformation material gets to deform easily due to repetition of being heated almost to a set temperature and has trouble with long-term reliability. Still further, the thermostat has the drawback that it is impossible to test repeatedly the thermal deformation material for the temperature when a fixed condition of the fuse springs is disengaged because the thermal deformation material can not return to its original shape once it has be en deformed by being heated. In addition to that, the thermostat has another drawback t hat the cost of parts is high and miniaturization is difficult since both of the fuse springs and thermal deformation material are housed therein.
The present invention was developed to solve these problems. It is thus a primary object of the present invention to provide a thermostat that can solve above-mentioned problems and a battery pack that contains the thermostat.
The above and further object of the invention will be more fully be apparent from the following detailed description with accompanying drawings,
The thermostat of the present invention comprises a first laminated metal plate and a second laminated metal plate in which a plurality of metal layers having different rates of expansion are laminated. The first laminated metal plate has a movable contact. The second laminated metal plate is disposed in such a position as to put the first laminated metal plate in the off and on positions. The first off temperature and the second off temperature, which put the movable contact in the off position by causing the first and second laminated metal plates to deform, and the first return temperature and the second return temperature, which return the movable contact from the off position to the on position, are set respectively at different temperatures.
The thermostat of the present invention comprises the first laminated metal plate 1 and the second laminated metal plate 2 having the following structures:
(a) The first laminated metal plate 1 having the movable contact 3 becomes in the on state by causing the movable contact 3 to come in contact with a fixed contact 4 and becomes in the off state by separating the movable contact 3 from the fixed contact 4.
(b) When the ambient temperature exceeds the first off temperature, the first laminated metal plate 1 thermally deforms in the direction which the movable contact 3 is separated from the fixed contact 4,
(c) When the temperature falls below the first return temperature, a thermal deformation force acts on the first laminated metal plate 1 in the direction which the movable contact 3 comes in contact with the fixed contact 4.
(d) The second laminated metal plate 2 is disposed in such a position as to put the first laminated metal plate 1 to the off and on positions.
(e) When the temperature exceeds the second off temperature, the second laminated metal plate 2 thermally deforms in such a shape as to maintain the first laminated metal plate 1 in the off position.
(f) When the temperature falls below the second return temperature, the second laminated metal plate thermally deforms in such a shape as to return the first laminated metal plate 1 to the on position.
(g) The second off temperature is higher than the first off temperature and the second return temperature is lower than the first return temperature.
(h) When the temperature exceeds the first off temperature, the first laminated metal plate 1 becomes in the off position and when the temperature exceeds the second off temperature, the second laminated metal plate 2 maintains the first laminated metal plate 1 in the off state.
(i) When the thermostat is heated to the temperature between the first and second off temperatures, the first laminated metal plate 1 becomes in the off position. In this state, the first laminated metal plate 1 returns to the on position when the ambient temperature falls below the first return temperature.
(j) When the temperature exceeds the second off temperature, the second laminated metal plate 2 thermally deforms in such a shape as to maintain the first laminated metal plate 1 in the off position. In this state, the first laminated metal plate 1 does not return to the on position even if the temperature falls to the temperature between the first and second return temperatures. However, it returns the first laminated metal plate 1 to the on position when the temperature falls below the second return temperature.
A thermostat having the above-mentioned structures has the features that the structures are extremely simple and the thermostat return temperature when the ambient temperature drops after it has reached a high temperature and current has been cut off can be varied depending on the rising temperature. This is because the thermostat comprises the first laminated metal plate and the second laminated metal plate in which a plurality of metal layers having different rates of expansion are laminated, the first laminated metal plate is provided with the movable contact, the second laminated metal plate is disposed in such a position as to put the first laminated metal plate in the off and on positions, and the first off temperature and the second off temperature, which put the first and second laminated metal plates in the off position by causing them to deform thermally, and the first return temperature and the second return temperature, which return the first and second laminated metal plates from the off position to the on position, are set respectively at different temperatures.
Further, in the thermostat, the second off temperature is higher than the first off temperature and the second return temperature is lower than the first return temperature. For this reason, when the ambient temperature exceeds the first off temperature, the first laminated metal plate becomes in the off position and cuts off current, and when the temperature falls below the first return temperature, the first laminated metal plate returns to the on position and turns on current. Still further, when the temperature exceeds the second off temperature, the first laminated metal plate does not return to the on position and current can be maintained in the cut-off state even if the temperature falls below the first return temperature because the second laminated metal plate maintains the first laminated metal plate in the off state. Therefore, the thermostat can firmly maintain current in the cut-off state after the temperature has risen abnormally. This thermostat can return the first laminated metal plate to the on position by returning the second laminated metal plate when the temperature falls to the second return temperature that is lower than the first return temperature.
Furthermore, the thermostat of the present invention can also comprise the first laminated metal plate 1 and the second laminated metal plate 2 having the following structures.
(a) The first laminated metal plate 1 having the movable contact 3 becomes in the on state by causing the movable contact 3 to come in contact with the fixed contact 4 and becomes in the off state by separating the movable contact 3 from the fixed contact 4.
(b) When the ambient temperature exceeds the first off temperature, the first laminated metal plate 1 thermally deforms in the direction which the movable contact 3 is separated from the fixed contact 4.
(c) When the temperature falls below the first return temperature, the first laminated metal plate 1 thermally deforms in the direction which the movable contact 3 comes in contact with the fixed contact 4.
(d) The second laminated metal plate 2 is disposed in such a position as to put the first laminated metal plate 1 in the off and on positions.
(e) When the temperature exceeds the second off temperature, the second laminated metal plate 2 causes the first laminated metal plate 1 to deform in the off position.
(f) When the temperature falls below the second return temperature, the second laminated metal plate 2 returns the first laminated metal plate 1 to the on position.
(g) The second off temperature is lower than the first off temperature and the second return temperature is higher than the first return temperature.
(h) When the temperature exceeds the second off temperature, the second laminated metal plate 2 puts the first laminated metal plate 1 in the off position, and when the temperature exceeds the first off temperature, the first laminated metal plate 2 thermally deforms by itself and becomes in the off position.
(i) When the thermostat is heated to the temperature between the first and second off temperatures, the second laminated metal plate 2 puts the first laminated metal plate 1 in the off position. In this state, the second laminated metal plate 2 returns and puts the first laminated metal plate 1 in the on position when the temperature falls below the second return temperature.
(j) When the temperature exceeds the first off temperature, the first laminated metal plate 1 thermally deforms in the off position. In this state, the first laminated metal plate 1 does not return to the on position even if the temperature falls to the temperature between the first and second return temperatures. However, the first laminated metal plate 1 thermally deforms and returns to the on position when the temperature falls below the first return temperature.
In this thermostat, the second off temperature is lower than the first off temperature and the second return temperature is higher than the first return temperature. For this reason, when the ambient temperature exceeds the second off temperature, the second laminated metal plate puts the first laminated metal plate in the off position and cuts off current, and when the temperature falls below the second return temperature, the second laminated metal plate returns the first laminated metal plate to the on position and turns on current. Further, when the temperature exceeds the first off temperature, the first laminated metal plate deforms by itself and becomes in the off position. Therefore, the first laminated metal plate does not return to the on position and current can be maintained in the cut-off state even if the second laminated metal plate returns to the on position when the temperature falls below the second return temperature. This thermostat can return the first laminated metal plate to the on position when the temperature falls to the first return temperature that is lower than the second return temperature.
As mentioned above, the thermostat of the present invention can be simplified In construction by the first and second laminated metal plates having special structures, and distinguish the cut-off and turned-on states of current and control them depending on the rising temperature. Therefore, the thermostat of the present invention can realize the features that miniaturization can be obtained by decreasing the number of parts compared with a prior art thermostat, and a large quantity of production at low cost can be obtained by reducing manufacturing steps. Furthermore, the thermostat of the present invention has the feature that the current cutoff state can be ideally controlled by setting the first and second off temperatures and the first and second return temperatures at suitable temperatures for the purposes, and it is possible to provide superior products in safety.
Further, the above-mentioned thermostat has another feature that deterioration of thermal deformation materials caused by repetition of being heated can be drastically reduced, and the long-term high reliability and safety are guaranteed unlike a prior art thermostat using thermal deformation materials. This is because the current cut-off and turned-on states are controlled by utilizing the first and second laminated metal plate thermal deformation.
Still further, the above-mentioned thermostat has another feature that it is possible to repeatedly test the first and second laminated metal plates for the temperature when current is cut off and turned on since the first and second laminated metal plates return to their original shapes at set temperatures. Thus, the thermostat in which the temperature test can be repeatedly conducted can improve the quality and raise the reliability.
The battery pack of the present invention contains the above-mentioned thermostat which cuts off current flowing to the batteries when the battery temperature reaches a high temperature.
In this battery pack, when the battery temperature rises to the first off temperature or the second off temperature, the thermostat cuts off current flowing to the batteries, and then it returns to the on state and turns on current when the temperature drops. For this reason, when the battery temperature reaches a high temperature, the thermostat cuts off current and prevents the temperature from becoming even higher than the high temperature. However, the thermostat returns the battery pack to a usable state after the temperature has fallen and the battery pack has become safe to use. Thus, the battery pack can return to the usable state without exchanging any parts unlike a fuse when the battery temperature fails to the battery pack usable temperature after the temperature has reached a high temperature.
Furthermore, in the battery pack described above, the thermostat can be so structured as not to easily return to the on state after current has been cut off by an abnormal rise in temperature which is caused by being over-charged or over-discharged in extreme situations, being used in shorted electric appliances or being used in extremely over-loaded situations. For this reason, the battery pack has the feature that it is extremely safe to use because current is maintained in the cut-off even if the battery temperature falls after the battery pack has been used in dangerous situations.